Power transmission device with at least two planetary gear trains

ABSTRACT

The invention concerns a power transmission device between a heat engine ( 1 ) and the wheels ( 2 ) of a motor vehicle, said device comprising two independent electric machines (3, 4), at least two planetary gear trains ( 5, 15, 25, 35; 6, 16, 26, 36 ) connecting the heat engine and the electric machines with one another and to the vehicle wheels, a mechanical switching device ( 7 ) shifting the transmission device from one operating mode to another, each transmission mode corresponding to a different range of transmission ratios, the switching device enabling to connect one of the electric machines directly to the vehicle wheels and a control device monitoring the heat engine ( 1 ), the two electric machines ( 3,4 ) and the mechanical switching device ( 7 ), so that the operating points of the heat engine and of the electric machines correspond to the minimum instantaneous consumption and enable to provide the required power to the wheels.

The invention relates to a transmission device for a motor vehicle,intended to ensure the transmission of power between the heat engine andthe wheels of the vehicle, while eliminating interruptions in torque.

Transmission members of this type are already known, for exampleautomatic gearboxes or members of the CVT (Continuous VariableTransmission) type or else of the IVT (Infinitely Variable Transmission)type, that is to say a transmission member making it possible to achieveall the transmission ratios contained in a determined interval.

These transmission members make it possible to place the heat engine atits best operating point by matching the transmission ratio to therunning conditions.

However, these members all have the drawback of entailing highconsumption since they exhibit a gearbox spread that is limited.Moreover, the absence of any interruption in torque is obtained bydissipating energy with loss in the clutches, couplers or hydraulicmachines.

A transmission member has already been tailored so as to overcome thisdrawback, as well to improve longitudinal comfort, as compared with anautomatic gearbox or a CVT transmission member, in its startup phase.

This transmission member, used by TOYOTA on the PRIUS vehicle, comprisestwo electric machines, a planetary gear train by way of which the heatengine and the two electric machines are connected together, as well asa battery. This transmission member operates according to the principleof power tapping which makes it possible to modulate the powertransmitted to the wheels.

When the heat engine is operating, part of its power is transmitteddirectly and mechanically to the wheels of the vehicle, while anotherpart of its power is “tapped off” by way of the two electric machines.

The power tapped off to the electric machines can be transmitted to thebattery or else to the wheels of the vehicle.

This transmission member also makes it possible to operate one of theelectric machines as a generator, in a slowdown phase, so as to transmitpower to the battery.

Such a transmission member makes it possible to obtain all thetransmission ratios in a given interval, while reducing consumption byaround 40% as compared with a conventional automatic gearbox, inparticular by virtue of the absence of any energy-dissipating clutch.

This member has the drawback however of being expensive, in particularowing to the presence of the battery. Moreover, the electric pathwayexhibits poor efficiency.

Document EP-1 092 583 describes a power unit for a vehicle whichcomprises a heat engine, a supervisor, an electromagnetic couplergrouping together two electric machines as well as one, or even twoplanetary gear trains.

This coupler is designed in a specific manner, the rotor of one machinebeing carried by the stator of the other machine, the two machines beingmoreover concentric.

This power unit affords a solution to the problem of the dimensioning ofelectric machines and to that of electric losses at zero speed of thecoupler.

It has drawbacks, however.

Specifically, it firstly requires the design of a specificelectromagnetic coupler consisting of two nested electric machines, thecost of which is necessarily high.

Moreover, the link between the two electric machines is established in amechanical and permanent manner, and not by way of planetary geartrains. This arrangement necessarily limits the available operatingmodes and hence in particular the possibility of optimizing consumption.

Likewise, the permanent link between the heat engine and the couplerlimits the operation of the assembly.

Finally, the switching device comprises dissipative elements such as aband brake or a clutch which necessarily entail losses and does not makeit possible to ensure continuity of the torque delivered to the wheels.

Document DE-199 03 936 relates to a transmission device for a motorvehicle equipped with a heat engine, this transmission device comprisingtwo electric machines, each being coupled up to at least one planetarygear train.

A mechanical switching device is also provided.

This device is designed in such a way that the electric machines are notcoupled up either to the crankshaft of the heat engine, or to thewheels. These links can be effected only by way of a planetary geartrain.

This transmission device has numerous drawbacks.

Specifically, the presence of an intermediate planetary gear trainbetween an electric machine and the wheels requires, during the startingof the vehicle, a considerable torque on an output of the train whichmust be delivered by the heat engine or by a brake. This is notdesirable, especially in terms of consumption.

Moreover, the operation of this transmission device requires thepresence of brakes at input and output.

An object of the invention is to improve the known transmission devicesfor hybrid vehicles by further reducing consumption, overall size andcosts, doing so in particular by using standard electric machines and bymaking the presence of power batteries unnecessary.

The invention therefore relates to a device for power transmissionbetween the heat engine and the wheels of a motor vehicle, the devicecomprising two independent electric machines, at least two planetarygear trains connecting the heat engine and the electric machinestogether and to the wheels of the vehicle, a mechanical switching deviceproviding for the shift from one mode of operation of the transmissiondevice to another, each mode of transmission corresponding to adifferent range of transmission ratios, the switching device making itpossible to connect one of the electric machines directly to the wheelsof the vehicle and a drive device controlling the heat engine, the twoelectric machines and the mechanical switching device, in such a waythat the operating points of the heat engine and of the electricmachines correspond to the minimum instantaneous consumption and make itpossible to obtain the requested power at the wheels.

This transmission device makes it possible to reduce consumption byvirtue of the presence of more than one planetary gear train, therebymaking it possible to reduce the electric power tapped off.

Preferably, the mechanical switching device includes no dissipativeelement and makes it possible to limit or eliminate jerks when shiftingfrom one mode of operation to another.

Thus, the transmission device then allows a further reduction inconsumption.

According to the invention, the mechanical switching device is placedbetween one of the two electric machines and the remainder of thetransmission device.

Preferably, the mechanical switching device allows the choice betweentwo different modes of operation.

In a preferred embodiment of the invention, the transmission devicecomprises two planetary gear trains whose three shafts are free inrotation with respect to the body of the vehicle and to the casing ofthe engine.

In a first variant, the two planet gear carriers are connected togetherand to the wheels.

One of the electric machines can then be connected, by way of themechanical switching device, either to the wheels of the vehicle, or tothe sun gear of one of the two planetary gear trains.

In a second variant, the planet gear carrier of the first planetary geartrain is connected to the ring gear of the second planetary gear trainand to the wheels.

One of the electric machines can then be connected, by way of theswitching device, either to the ring gear, or to the sun gear of thesecond planetary gear train.

In a third variant, the ring gear of the first planetary gear train isconnected to the planet gear carrier of the second planetary gear trainand to the wheels.

One of the electric machines can then be connected, by way of theswitching device, either to the sun gear of the first planetary geartrain, or to the planet gear carrier of the second planetary gear train.

In a fourth variant, the sun gear of the first train is connected to thering gear of the second train and to the wheels.

One of the electric machines can then be connected, by way of theswitching device, either to the sun gear, or to the planet gear carrierof the first planetary gear train.

Moreover, the ratios of the two planetary gear trains are chosen in sucha way that, when the speed of the output shaft of said electric machineis equal to the speed of the sun gear of said planetary gear train, thespeed of the output shaft of the other electric machine is zero.

Preferably, the mechanical switching device with no dissipative elementis a jaw clutch.

The invention also relates to a process for transmitting power betweenthe heat engine and the wheels of a motor vehicle, by means of twoindependent electric machines, of at least two planetary gear trainsconnecting the heat engine and the electric machines together, and of amechanical switching device making it possible to connect one of theelectric machines to the wheels of the vehicle, this process consistingin determining the transmission ratio, in commanding the switchingdevice so as to ensure the transmission according to the modecorresponding to said ratio and in controlling the heat engine and thetwo electric machines, in such a way that the operating points of theheat engine and of the electric machines correspond to the minimuminstantaneous consumption and make it possible to obtain the requestedpower at the wheels.

Preferably, the mechanical switching device includes no dissipativeelement.

According to the invention, the shift from one mode of operation to theother is performed when the speed of the output shaft of the electricmachine connected to the mechanical switching device is equal to thespeed of the shaft connecting this mechanical switching device to theremainder of the transmission device.

Preferably, the shift from one mode of operation to the other isperformed when the power tapped off from the two electric machines iszero, so as to avoid an abrupt variation in torque.

The invention also relates to a motor vehicle equipped with a powertransmission device as described above.

This motor vehicle can comprise a power battery.

The invention will be better understood and other aims, advantages andcharacteristics thereof will become more clearly apparent on reading thedescription which follows and which is given with regard to the appendeddrawings in which:

FIG. 1 is a diagrammatic view representing a first exemplary embodimentof a transmission device according to the invention comprising twoplanetary gear trains,

FIG. 2 is a diagram illustrating the operation of the transmissiondevice of FIG. 1, in a first mode,

FIG. 3 is a diagram illustrating the operation of the device of FIG. 1,in a second mode

FIG. 4 is a diagrammatic view representing a second exemplary embodimentof a transmission device according to the invention,

FIG. 5 is a diagrammatic view representing a third exemplary embodimentof a transmission device according to the invention,

FIG. 6 is a diagrammatic view representing a fourth exemplary embodimentof a transmission device according to the invention and

FIGS. 7 to 10 which give, for the first exemplary embodiment of atransmission device according to the invention and during accelerationof the motor vehicle, the time dependent profile, respectively of thetorque of each electric machine, (C₃, C₄), of the rate of each machine(N₃, N₄), of the electric power tapped off (P) and of the speed of thevehicle.

The elements common to the various figures will be designated by thesame references.

The transmission device illustrated in FIG. 1 is intended for a motorvehicle comprising a heat engine 1. The wheels of the vehicle arereferenced 2.

The transmission device comprises two electric machines 3 and 4.

The heat engine 1 and the electric machines 3 and 4 are connectedtogether by way of two planetary gear trains 5 and 6.

The planetary gear train 5 is connected by way of its sun gear 50 to theoutput shaft 10 of the heat engine 1.

Its planet gear carrier 51 is connected to the output shaft 20 connectedto the wheels 2. The planet gears bear the reference 510.

Finally, the electric machine 3 meshes with the ring gear 52 of thefirst train 5 by way of the toothed wheels 81 and 82. The machine 3 isconnected to the toothed wheel 81 by its output shaft 30.

The output shaft 10 of the heat engine 1 is also connected to the ringgear 62 of the second train 6.

The planet gear carrier 61 is connected to the planet gear carrier 51and to the output shaft 20. The planet gears bear the reference 610.

Finally, the sun gear 60 of the second train 6 can be connected to theelectric machine 4, by means of a mechanical switching device 7represented very diagrammatically in FIG. 1, and by way of the shafts 40and 41 of the toothed wheels 83 and 84.

Preferably, this mechanical switching device comprises no dissipativeelements. It may in particular take the form of a dog jaw clutch.

Finally, the electric machine 4 can also be connected, still by way ofthe mechanical switching device 7, to the output shaft 20, by way of thetoothed wheels 85 and 86.

Thus, in this transmission device, the mechanical switching device 7 isplaced between one of the two electric machines 4 and the remainder ofthe transmission device. In practice, this transmission device takes theform of a single jaw clutch.

Moreover, the two planetary gear trains 5 and 6 are designed in such away that the two planet gear carriers 51 and 61 are connected togetherand to the wheels.

Thus, the link between the heat engine and the electric machines andbetween the electric machines is effected by way of the two planetarygear trains.

In particular, there is no fixed link between the heat engine and one orthe other of the electric machines, so as to have great flexibility inthe choice of operating modes.

The operation of the transmission device will now be described firstlywith reference to FIG. 2 which illustrates a first mode of operation.

This first mode of operation is used for relatively low transmissionratios. They may in particular correspond to a speed of between 0 and 15kilometres/hour (output shaft 20 connected to the wheels) for a speed ofthe heat engine 1 of 1000 rpm.

This first mode of operation is therefore used in particular during thestarting of the vehicle.

In this mode of operation, the electric machine 4 is connected, by wayof the toothed wheels 85 and 86, to the output shaft 20, constitutingthe secondary shaft of the transmission. The switching device 7 isactuated in an appropriate manner such that the toothed wheel 86 isengaged on the shaft 40.

The electric machine 4 is thus directly engaged with the output shaft 20and hence the wheels of the vehicle. This direct link is effectedwithout losses. Moreover, it allows an electric machine to generate aconsiderable torque at the level of the wheels with a machine ofrelatively small dimensions.

The second planetary gear train 6 is represented by dashes in FIG. 2.Specifically, the ring gear 62 of this train 6 is driven well by theheat engine 1, but does not transmit power to the wheels since it is notconnected to the output shaft 20.

Thus, the toothed wheel 86 drives the output shaft 20 connected to thewheels 4, by way of the toothed wheel 85, whereas the toothed wheel 84is idling.

In this mode of operation, the speed of the output shaft 20 is equal tothe speed of the planet gear carriers 51 and 61 of the two planetarygear trains.

When the vehicle is under traction, that is to say when the heat engineis delivering power to the wheels, the electric machine 3 operates as analternator while the electric machine 4 is a motor. When the vehicle isin recovery, that is to say the wheels are driving the heat engine inrotation, the electric machine 3 operates as a motor and the electricmachine 4 as an alternator.

A link device, not illustrated in the figures, ensures the shifting ofpower between the two electric machines.

Such a link device is described in particular in the document FR-0009461.

It may also be noted that the transmission device is used according tothe first mode of operation, when the vehicle is reversing.

Reference is now made to FIG. 3 which illustrates a second mode ofoperation of the transmission device illustrated in FIG. 1.

This second mode of operation is used for relatively long transmissionratios, corresponding for example to a speed of the output shaft ofbetween 15 and 60 kilometres/hour for a speed of the heat engine of 1000rpm.

This second mode of operation is used when the vehicle is travellingforwards, after startup.

In this second mode of operation, the mechanical switching system 7 isinstructed in such a way as to connect the electric machine 4 to thetoothed wheel 84, then engaged with the shaft 41, the wheel 86 thenidling. The shafts 40 and 41 are then tied in rotation by way of thedevice 7.

The wheels 85 and 86 are represented by dashes in FIG. 3 to illustratethe fact that they do not transmit power to the wheels.

The electric machine 4 then meshes with the sun gear 60 of the secondplanetary gear train 6, by way of the wheels 84 and 83.

Moreover, the heat engine 1 is still connected to the sun gear 50 of thefirst planetary gear train 5 and the electric machine 3 still mesheswith the ring gear 52 of this first train, by way of the wheels 81 and82.

As explained previously for the first mode of operation, the electricmachines 3 and 4 can operate as a motor or alternator, as the case maybe.

A drive device, not illustrated in the figures, controls the heat engineand the two electric machines by determining their operating point andalso controls the mechanical switching device 7 in the following manner.

On the basis of charts of instantaneous consumption of the heat engineas well as charts of efficiency of the electric machines, the drivedevice determines the operating point of the heat engine and of theelectric machines which corresponds to the minimum instantaneousconsumption and which ensures that the torque obtained at the wheelsdoes indeed correspond to what the driver requires.

If the drive device detects a minimum consumption for a relatively lowtransmission ratio, the power transmission device is used according tothe first mode of operation and, in this case, the mechanical switchingdevice 7 is instructed in such a way that the wheel 86 is locked to theoutput shaft 40 of the electric machine 4. Otherwise, the transmissiondevice is used in the second mode of operation and the mechanicalswitching device 7 is then instructed in such a way that the outputshaft 40 of the electric machine 4 is connected to the wheel 84, hencelocked to the shaft 41.

In practice, the shift from one mode of operation to another is effectedwhen the speed of the output shaft 40 of the electric machine 4 is equalto the speed of the shaft 41 connecting the switching device 7 to thetoothed wheel 84. The continuity of the rates is necessary in order forthe switching device to be able to operate.

To within the reduction ratio, due to the presence of the toothed wheels83 and 84, this condition is also achieved when the speed of the outputshaft 40 of the electric machine 4 is equal to the speed of the sun gear60 of the planetary gear train 6.

When shifting from mode of operation to another, the torque on theoutput shaft 20 decreases, thereby generating an abrupt jerk.

Several solutions may be envisaged for limiting or eliminating this jerkduring a change of operating mode.

Provision may in particular be made for the drive device to instruct theelectric machine 3 appropriately, during a change of operating mode, sothat this machine delivers a bigger torque for a determined duration, tocompensate for the absence of torque originating from the electricmachine 4.

Another solution consists in choosing the ratios of the planetary geartrains 5 and 6 in such a way that when the continuity condition on therates is fulfilled, the speed of the output shaft 30 of the electricmachine 3 is zero.

This condition is also manifested by the fact that the power tapped fromthe two electric machines 3 and 4 is zero.

The stopping of the electric machine 3 during the change of rate makesit-possible to minimize the torque delivered by the electric machine 4.This torque is not zero however, owing to the losses in the electricmachines and to the consumption in the onboard network.

This condition being achieved, provision may be made for the drivedevice to instruct the heat engine and/or the electric machine 3appropriately in such a way as to generate a slightly bigger torque soas to ensure the continuity of the torque delivered to the wheels.

By applying the WILLIS relation to each of the two planetary geartrains, the stopping of the electric machine 3 during a change ofoperating mode is manifested by the following condition:[r ₃/(r ₂ R ₂)−(R ₂+1)/R ₁+(R ₁+1)]=0with:

-   -   r₃=Z₄/Z₃ where Z₃ and Z₄ are respectively the number of teeth of        the toothed wheels 83 and 84,    -   r₂=Z₆/Z₅ where Z₅ and Z₆ are respectively the number of teeth of        the toothed wheels 85 and 86,

-   R₂ is the ratio of the planetary gear train 6,

-   R₁ is the ratio of the planetary gear train 5.

The presence of an additional planetary gear train, as compared with theknown transmission devices with a single planetary gear train, makes itpossible to operate the transmission device according to an additionalmode of operation.

This additional mode of operation makes it possible to operate the heatengine and the electric machines with better efficiency, in a biggerrange of transmission ratios.

This is manifested by the fact that the electric power tapped off by wayof the two electric machines decreases.

By way of example, as compared with a conventional transmission member,for which the maximum power tapped off is of the order of 50 kW, thispower tapped off is of the order of 17 kW for a transmission device suchas described above, this being so for equivalent performance.

Thus, the transmission device according to the invention makes itpossible to ensure the continuity of the torque at the wheels and henceto eliminate jerks, while delivering the power requested to the wheelswith minimum consumption.

By way of illustration of the advantages afforded by the transmissiondevice according to the invention, FIGS. 7 to 10 show the time dependentprofile of the torque and of the rate of each of the two electricmachines, as well as the time dependent profile of the power tapped offand of the speed of the vehicle, during acceleration of the vehicle.

At the time t=0 up to the time t=9.5 seconds, it is the first mode ofoperation described with reference to FIG. 2 which is used.

The shift to the second mode of operation is carried out at t=9.5seconds, while the rate of the electric machine 3 (N₃) is zero and thetorque delivered by the electric machine 4 (C₄) is zero. At thatinstant, the power tapped off from the two electric machines 3 and 4 (P)is likewise zero.

FIGS. 7 to 10 show that the transmission device according to theinvention ensures continuity of the torque and of the rate of each ofthe two electric machines.

It ensures considerable longitudinal dynamics with electric machineswhose dimensional sizes are moderate by virtue of the substantialadaptability afforded by the mechanical part.

Other exemplary embodiments of the switching device according to theinvention are illustrated in FIGS. 4 to 6.

Of course, the invention is not limited to a transmission devicecomprising two planetary gear trains. It would also be possible toenvisage a power transmission device comprising three planetary geartrains, or even more. The number of planetary gear trains is essentiallylimited by cost reasons.

In the second exemplary embodiment illustrated in FIG. 4, the heatengine 1 and the electric machines 3 and 4 are connected together by wayof two planetary gear trains 15 and 16.

The planetary gear train 15 is connected by way of its sun gear 150 tothe output shaft 10 of the heat engine.

Its planet gear carrier 151 is connected to the ring gear 162 of thesecond planetary gear train 16 and to the output shaft 20 connected tothe wheels 2. The planet gears bear the reference 1510.

The electric machine 3 meshes with the ring gear 152 of the firstplanetary gear train 15 by way of the toothed wheels 81 and 82. Themachine 3 is connected to the toothed wheel 82 by its output shaft 30.

The output shaft 10 of the heat engine 1 is likewise connected to theplanet gear carrier 161 of the second planetary gear train 16. Theplanet gears bear the reference 1610.

The ring gear 162,of the second planetary gear train 16 can likewise beconnected to the electric machine 4, by means of the mechanicalswitching device 7 and by way of the shaft 40 of the electric machine 4and of the toothed wheels 85 and 86.

Finally, the sun gear 160 of the second planetary gear train canlikewise be connected to the electric machine 4, by means of themechanical switching device 7 and by way of the shafts 40 and 41 and ofthe toothed wheels 83 and 84.

As in the first exemplary embodiment, the mechanical switching device isplaced between one of the two electric machines and the remainder of thetransmission device. It is composed, for example, of a single jawclutch.

In the third exemplary embodiment illustrated in FIG. 5, the heat engine1 and the electric machines 3 and 4 are connected together by way of twoplanetary gear trains 25 and 26.

The first planetary gear train 25 is connected by way of its planet gearcarrier 251 to the output shaft 10 of the heat engine 1 and to the ringgear 262 of the second planetary gear train 26. The planet gears bearthe reference 2510.

Its sun gear 250 can be connected to the electric machine 4 by means ofthe mechanical switching device 7 and by way of the shafts 40 and 41 andof the toothed wheels 83 and 84.

The ring gear 252 of the first planetary gear train 25 is connected tothe planet gear carrier 261 of the second planetary gear train 26 and tothe output shaft 20 connected to the wheels 2. The planet gears bear thereference 2610.

It may also be connected to the electric machine 4, by means of themechanical switching device 7 and by way of the toothed wheels 85 and86.

Finally, the sun gear 260 of the second planetary gear train 26 isconnected to the electric machine 3 by way of the toothed wheels 81 and82 and of the output shaft 30.

Here again, the mechanical switching device is placed between one of thetwo electric machines and the remainder of the transmission device andmay then be constituted by a single jaw clutch.

With reference now to FIG. 6, the heat engine 1 and the electricmachines 3 and 4 are connected together by way of two planetary geartrains 35 and 36.

The first planetary gear train 35 is connected by way of its sun gear350 to the ring gear 362 of the second planetary gear train 36.

Through its sun gear 350, the train 35 can also be connected to theelectric machine 4, by means of the switching device 7 and by way of thetoothed wheels 85 and 86.

In this case, the electric machine 4 drives the wheels 2 directly.

The ring gear 352 of the train 35 is connected to the output shaft 10 ofthe heat engine 1, which is also connected to the sun gear 360 of thesecond planetary gear train 36.

Moreover, the planet gear carrier 351 of the train 35 can be connectedto the electric machine 4, by means of the mechanical switching device 7and by way of the toothed wheels 83 and 84 and of the shafts 40 and 41.The planet gears bear the reference 3510.

In this case, the electric machine 4 serves as variator motor for thefirst train 35 and the power is transmitted to the wheels by the toothedwheels 85, 86 and 87.

The planet gear carrier 361 of the second planetary gear train 36 isconnected to the electric machine 3 by way of the toothed wheels 81 and82 and of the shaft 30. The planet gears bear the reference 3610.

Here again, the switching device 7 is placed between one of the twoelectric machines and the remainder of the transmission device. Inpractice, it may take the form of a jaw clutch.

In all the embodiments described, the planetary gear trains make itpossible to connect together the electric machines and also the heatengine.

There are no fixed links that could limit the choice of operating modes.

In all cases, the three shafts of the planetary gear trains are free inrotation with respect to the body of the vehicle and to the casing ofthe engine. This has the advantage of providing a large number ofpossible combinations for optimizing the dimensional sizing of theelectric machines.

Moreover, the electric machines used are independent and may be standardmachines, of simple construction and whose manufacturing costs areoptimized, like those intended for air-conditioning compressors orpumps.

With each planetary gear train may be associated a particular mode ofoperation of the power transmission device.

As described above, the transmission device comprises mechanicalelements other than the planetary gear trains, such as for exampletoothed wheels catering only for the transmission of movements. However,it does not require elements such as brakes to cater for the operationof the device in all modes.

Moreover, the use of a mechanical switching device, with no dissipativeelement, also makes it possible to reduce consumption.

In the exemplary embodiments described, the switching device is disposedbetween an electric machine and the remainder of the transmissiondevice.

Thus, the switching device can in particular take the form of a singlejaw clutch. The control software associated with the drive device istherefore designed to control just one jaw clutch and it is necessarilya simpler design than software driving several jaw clutches.

Moreover, in this configuration, the switching device offers the choicebetween two different modes of operation.

This power transmission device can be used with a motor vehiclecomprising or not comprising a battery.

The presence of a battery has the benefit of reducing consumption whenthe vehicle is operating at low power.

However, a battery has drawbacks especially in terms of bulkiness andcost. It is thus possible to choose not to make provision for one.

In practice, and independently of the transmission device, the presenceof batteries is determined according to the driving strategy chosenduring the design of the vehicle.

In this case, a link device ensures direct shifting of power between thetwo electric machines, the electric machines being controlled in such away that the power generated by one electric machine is immediatelyconsumed by the other.

Such a link device is described in particular in the document FR-0009461.

The reference signs inserted after the technical characteristicsfeatured in the claims have the sole aim of facilitating theirunderstanding and shall not limit the scope thereof.

1. A device for power transmission between a heat engine (1) and wheels(2) of a motor vehicle, the device comprising two independent electricmachines (3, 4), at least two planetary gear trains (5, 15, 25, 35; 6,16, 26, 36) connecting the heat engine and the electric machinestogether and to the wheels of the vehicle, a mechanical switching device(7) providing for the shift from one mode of operation of thetransmission device to another, each mode of transmission correspondingto a different range of transmission ratios, the switching device (7)making it possible to connect one of the electric machines (4) directlyto the wheels (2) of the vehicle and a drive device controlling the heatengine (1), the two electric machines (3, 4) and the mechanicalswitching device (7), in such a way that the operating points of theheat engine and of the electric machines correspond to the minimuminstantaneous consumption and make it possible to obtain the requestedpower at the wheels.
 2. The power transmission device as claimed inclaim 1, characterized in that the mechanical switching device (7)includes no dissipative element and makes it possible to limit oreliminate jerks when shifting from one mode of operation to another. 3.The power transmission device as claimed in claim 1 or claim 2, in whichthe mechanical switching device (7) is placed between one of the twoelectric machines (4) and the remainder of the transmission device. 4.The power transmission device as claimed in claim 1, in which themechanical switching device allows the choice between two differentmodes of operation.
 5. The power transmission device as claimed in claim1, comprising two planetary gear trains (5, 6; 15, 16; 25, 26; 35, 36)whose three shafts are free in rotation with respect to the body of thevehicle and to the casing of the engine.
 6. The power transmissiondevice as claimed in claim 5, in which the two planet gear carriers (51,61) for said two planetary gear trains (5, 6; 15, 16; 25, 26; 35, 36)are connected together and to the wheels (2).
 7. The power transmissiondevice as claimed in claim 6, in which one of the electric machines (4)can be connected, by way of the mechanical switching device (7), eitherto the wheels (2) of the vehicle, or to a sun gear (60) of one of thetwo planetary gear trains (6).
 8. The power transmission device asclaimed in claim 5, in which a planet gear carrier (151) of the firstplanetary gear train (15) is connected to a ring gear (162) of thesecond planetary gear train (16) and to the wheels (2).
 9. The powertransmission device as claimed in claim 8, in which one of the electricmachines (4) can be connected, by way of the switching device (7),either to the ring gear (162), or to a sun gear (160) of the secondplanetary gear train (6).
 10. The power transmission device as claimedin claim 5, in which a ring gear (252) of the first planetary gear train(25) is connected to a planet gear carrier (261) of the second planetarygear train (26) and to the wheels (2).
 11. The power transmission deviceas claimed in claim 10, in which one of the electric machines (4) can beconnected, by way of the switching device (7), either to a sun gear(250) of the first train (25), or to the planet gear carrier (261) ofthe second train (26).
 12. The power transmission device as claimed inclaim 5, in which a sun gear (350) of the first train (35) is connectedto a ring gear (362) of the second train (36) and to the wheels (2). 13.The power transmission device as claimed in claim 12, in which one ofthe electric machines (4) can be connected, by way of the switchingdevice (7), either to the sun gear (350), or to a planet gear carrier ofthe first planetary gear train (35).
 14. The power transmission deviceas claimed in claim 5, in which the ratios of the two planetary geartrains (5; 6) are chosen in such a way that, when the speed of theoutput shaft (40) of said electric machine (4) is equal to the speed ofa sun gear (60) of said planetary gear train (6), the speed of an outputshaft (30) of the other electric machine (3) is zero.
 15. The powertransmission device as claimed in claim 2, in which the mechanicalswitching device (7) is a jaw clutch.
 16. A process for transmittingpower between a heat engine (1) and wheels (2) of a motor vehicle, bymeans of two independent electric machines (3, 4), of at least twoplanetary gear trains (5, 15, 25, 35; 6, 16, 26, 36) connecting the heatengine and the electric machines together, and of a mechanical switchingdevice (7) making it possible to connect one of the electric machines(4) to the wheels (2) of the vehicle, this process consisting indetermining the transmission ratio, in commanding the switching deviceso as to ensure the transmission according to the mode corresponding tosaid ratio and in controlling the heat engine and the two electricmachines, in such a way that the operating points of the heat engine andof the electric machines correspond to the minimum instantaneousconsumption and make it possible to obtain the requested power at thewheels.
 17. The process as claimed in claim 16, characterized in thatthe mechanical switching device includes no dissipative element.
 18. Theprocess as claimed in claim 16 or claim 17, in which the shift from onemode of operation to the other is performed when the speed of the outputshaft (40) of the electric machine (4) connected to the mechanicalswitching device is equal to the speed of a shaft (41) connectingmoreover this mechanical switching device to the remainder of thetransmission device.
 19. The process for transmitting power as claimedin claim 18, in which the shift from one mode of operation to the otheris performed when the power tapped off from the two electric machines iszero, so as to avoid an abrupt variation in torque.
 20. A motor vehicleequipped with a power transmission device as claimed in claim
 1. 21. Themotor vehicle as claimed in claim 20 comprising a power battery.